Which is better, too large or too small of a boiler?

blueaa

I am replacing the boiler for my single pipe steam system. My current boiler is 394 sq ft steam, which is slightly oversize for what I have calculated I need at about 384, but it didn't short-cycle. For the boilers I like this falls in between 2 models. The smaller one 354 sq ft ( 138,000 input BTU, 113,000 DOE BTU, 85,000 Net IBR BTU) and larger is 446 sq.ft. ( 172 input, 142 Output, 107 Net IBR). Which is a better choice? How small a difference is negligile? I have always heard the rule that you pick the one at or just above your steam needs, but this seems to be approaching oversize.



The price difference matters to me only because it makes it easier to use thermostatic vacuum breaker replacement valves.



Not sure it matters, but this is a wet return system and the new installation will have dual risers from the top of the boiler and swing joints, I will probably install drop head risers. I have lots of overhead room available above the water line so maybe that is just my usual frivolousness.



My current piping and venting to work great. I had to correct some hammer problems and a no main vent from 12 years ago when I moved in, mainly due to poor modifications made when the house was duplexed many years ago.

Rod

Boiler Sizing

Here's an article by a really knowledgeable Chicago steam pro, Dave Bunnell, which may be of help to you in making your choice.

http://www.heatinghelp.com/article/323/Boilers/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell

I'm assuming the 354 unit has the 1.33 pickup already factored in. My questions would be how well is your boiler piping insulated and how well does the present boiler heat the house when it gets really cold ?

- Rod

Bio

Boiler match

Looks like the Peerless 63-04L with 383 sqft steam matches your needs and follow Boilerpro method and you will be fine, my boiler matches my radiators edr and with all hoffman 40 my pressure never goes over 2oz, "Vent mains fast and radiators slow but full"